Metal salts having astringent properties are widely used to inhibit human axillary perspiration. While aluminum salts are most widely used, zinc salts have found some favor, and zirconium salts have recently become commercially important. Salts of many other metals have antiperspirant activity, but because of considerations of cost, availability, toxicity, color problems or the like, are not generally useful. Commonly used anions of the metal salts include the chloride or chloride and hydroxide, but other anions such as the sulfate, sulfamate, phenolsulfonate, bromide, iodide, nitrate, and lactate have been disclosed in the art as being useful.
One of the problems encountered in formulating antiperspirants based on acidic astringent metal salts is that fabrics with which they come into contact are often weakened. In addition, persons having sensitive or broken skin can experience irritation presumably caused by the low pH of such formulations. To overcome these problems, it is necessary to incorporate buffers such as urea and amino acids to adjust and control the pH. Sometimes basic metal salts can be employed to give a somewhat higher pH. In addition various active ingredients or additives intended to decrease fabric damage or increase mildness to the skin have been disclosed in the art. A further problem in the use of astringent metal salts is that the difficulty in preparing smooth, cosmetically acceptable formulations increases with increasing amounts of metal salt.
A further drawback in the use of astringent metal antiperspirants is the fact that considerable time can elapse between their application and the perception of their desired effect. The antiperspirant effect is not fully developed in most people for several hours, and maximum effectiveness is obtained only after regularly repeated usage over a period of days or weeks. Even more serious, a portion of the population is unable to achieve control of perspiration by the use of astringent metal salt antiperspirants. At best, such compositions, containing relatively large amounts of metallic salts, will provide about 40-50% reduction in perspiration in the axillae.
Anticholinergic agents have been used by the medical profession for the systemic and topical treatment of certain pathological cases of excessive sweating. They have also been suggested in the literature as possible ingredients of cosmetic antiperspirants.
In defining "anticholinergic," it is necessary to briefly describe certain aspects of human perspiration. Eccrine sweat glands, which secrete most of the liquid perspiration, are activated by a chemical mediator, usually considered to be acetylcholine, which is liberated at nerve endings when they are properly stimulated. An anticholinergic compound is one which destroys the action of the acetylcholine, probably by blocking the receptor sites of the secretory cells of the sweat glands, so that the cells are unable to respond. In addition to the eccrine glands, which are widely distributed over the surface of man's body, there are apocrine sweat glands which are fewer in number and are localized in particular areas including the axillae. Examples of anticholinergic compounds used in classical studies of perspiration inhibition include scopolamine and atropine.
In spite of the fact that such anticholinergics have been known to be useful in controlling human perspiration, satisfactory anticholinergic formulations for cosmetic and medical use have not been developed, the chief difficulty being to achieve adequate inhibition of perspiration at a level of usage which is physiologically safe.
A major problem in employing anticholinergic compounds heretofore for the control of human perspiration revolves about the mydriatic activity of such compounds on the eye. The risk of mydriasis has been especially great when anticholinergic compounds have been formulated as the active ingredient in antiperspirant products packaged in a manner presenting an increased risk of accidental instillation into the eye of the user. While it is possible to reduce the risk of mydriasis by reducing to a minimum the concentration of the active anticholinergic ingredient, it has generally been felt that the risks have outweighed the benefits.